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Thread: replacing cast iron radiator supplys

  1. #1

    Default replacing cast iron radiator supplys

    I need to relocate a couple of cast iron radiators in my own house. So before I turn the heat on in the house I would like to replace the pipes going to each radiator with barrier pex. I want to install a manifold for the supply and return. I am thinking a 1" manifold with 3/4" pex to each radiator.
    I am a builder so Iím not shy to try this myself, just want to make sure I do it right the first time before the cold gets here. Hard to say cold weather when it has not been out of the 90's for weeks now, but I need to get this done so any help is appreciated.

    Thanks
    Bill Bonetto
    Bonetto's Carpentry

  2. #2
    Moderator & Master Plumber hj's Avatar
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    Radiators are NOT like baseboard heat, so you have to be careful when you redo piping for them that you maintain flow and capacity. I am not sure HOW you intend to pipe to a manifold or to the radiators, but it might NOT be the right way to do it. More details might help.

  3. #3

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    Thanks for the reply. I'll try to be a little more specific. House is about 50+ years old. Currently I have the original 2" diameter two pipe system running down the basement ceiling from boiler in rear of house to the front of the house. When my boiler was replaced a year ago all the new plumbing they installed was 1" copper from the boiler increasing in size to the 2" supply and return. I would like to build a 1" manifold out of 1" copper with 1" x 1" x 3/4" Tee's. Out of the Tee's I would like to put a 3/4" full port ball valve. Then to each radiator use 3/4" pex and back to the return manifold. I do know that I would have to use a barrier pex. In my head I'm thinking this should work but you guys are the pros.

    Thanks
    Bill Bonetto
    Bonetto's Carpentry

  4. #4
    Moderator & Master Plumber hj's Avatar
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    Using 3/4" PEX means you would in effect feeding the radiators with ONE HALF INCH pipes, and that would be undersized for anything other than a very small cast iron radiator. In addition, you have to have enough resistance in the manifolds to force water into the radiator lines to get circulation. Modulating the valves would create resistance, but would also create an obstruction to the flow.

  5. #5
    In the Trades Wally Hays's Avatar
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    Here's the right way to do it.

    You want to run 1/2" heat pex from each radiator, back to manifolds near the boiler.( feeds & returns ) You can either split manifolds and pumps up to achieve zoning or you can use thermostatic radiator valves at the radiators or even zone valves off the manifold tee's. Make sure the manifolds are large enough to handle the flow ( 1" minimum but you can't go wrong going larger) Re-piping the boiler so that the circulator pumps towart the feed manifold will help in air elimination and also flow but it is not mandatory.
    Perception is 3/4 of reality

  6. #6

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    Hey guys thanks for the info. Definately taking it all in. The house is only one story and about 1000 sq'. The longest a supply run from the manifold to the furthest radiator would be no longer than 35'. It would just be one zone for the entire house. When I finally get to add a second floor I will change everything over to radiant floor. What does a zone valve do that a 3/4' ball valve doesnt. (im guessing opens and closes as each zone requires heat?) But if its only one zone for the whole house can I just put ball valves on the tee's?
    I could close off a ball valve slightly if one room gets to hot to reulate flow.

    Thanks
    Bill Bonetto
    Bonetto's Carpentry
    Last edited by williambonetto; 07-25-2010 at 05:59 PM.

  7. #7

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    duplicate post
    Last edited by williambonetto; 07-25-2010 at 06:00 PM. Reason: duplicate post

  8. #8
    In the Trades Wally Hays's Avatar
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    If it's only one zone then you don't need zone valves. A ball valve on the either the feed or return will allow you to regulate each radiator or even shut it off if you want.
    Perception is 3/4 of reality

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